Automatic tuning system



2 Sheets-Sheet 1 www@ G. L. BEERS AUTOMATIC TUNING SYSTEM Filed Feb. 23, 1954 July 29, 1941.

July 29,- l941- G. L. BEERSl 1 2,250,519

AUTOMATI C TUNING SYSTEM 'med Feb. 2s. 1934 2 Sheets-sheet 2 Patented July 29, 1941 UNITED STTES 25ans AUTMATIC TUNING SYSTEM George L. Beers, Collingswood, N. J., assignor to Radio Corporation cf America, a corporation of Delaware My invention relates to radio receivers, and more particularly to receivers of the superheterodyne type.

Recently, there has been a very decided trend toward the use in radio receivers of auxiliary apparatus for the purpose of obtaining automatic volume control. That is to say, means are provided for the derivation of a unidirectional potential proportional to the amplitude of an incoming carrier wave, and such potential is utilized to so bias certain of the thermionic tubes in the receiver that the gain therein is reduced concurrently with increase in signal amplitude.

While the use of automatic volume control devices elfectively minimizes the annoyance caused by fading, it renders the receiver somewhat difficult to tune. This diculty arises by reason of the fact that there is no abrupt change in the sound output from the receiver as it is tuned through exact resonance with an incoming carrier. If the receiver is not properly tuned, its signal output is of poor quality since a portion of the signal side bands are attenuated by the tuned intermediate frequency transformers.

It is, accordingly, an object of my invention to provide a radio receiver of the superheterodyne type that shall be substantially automatic insofar as tuning is concerned.

Another object of my invention is to provide an automatic tuning system for a radio receiver that shall have no deleterious effect upon the overall fidelity of the said receiver.

A still further object of my invention is to provide a radio receiver that may be manually tuned tc within a few kilocycles of resonance and which thereafter automatically tunes itself to receive the desired signal.

There are a number of ways in which the objects of my invention may be obtained. Perhaps the most simple manner in which the desired resuit may be accomplished is to use a receiver of the superheterodyne type and to provide means whereby the received signal is utilized to so control the oscillator frequency that the said signal automatically heterodynes itself to the correct intermediate frequency. This arrangement, however, does not give rise to satisfactory resuits, if sharply tuned radio frequency input circuits of conventional types are utilized, because,

when using such circuits, the alignment between the intermediate frequency and the radio frequency circuits cannot be shifted by as much as plus or minus three or four kilocycles without producing a serious effect upon the overall fidelity characteristic of the receiver.

In accordance with one embodiment of my invention, therefore, I provide a tunable filter input system which effectively passes a band of frequencies 25 or 50 kilocycles above and below the frequency of the desired signal. More specilically, I prefer to utilize aV tunable filter wherein only the inductance elements are varied for tuning purposes. Such a filter may include a plurality of inductors each of which has a movable lcore and means are provided for simultaneouslymoving the cores to thereby alter the effective inductance of the inductors with which they are a'ssociated.

Further, in accordance with my invention, I provide a thermionic device for controlling the local oscillator frequency, the measure of control being determined by the amount of departure of the intermediate frequency produced from a predetermined frequency.

In the preferred embodiment of my invention, I add a speciallydesigned noise suppressor circuit to the rst-mentioned embodiment whereby the operation of the automatic tuning circuit is improved.

The novel features that I consider chars cteristic of my invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation, together with additional objects iand advantages thereof, will best be understood from the-following description of a specific embodiment, when read in connection With the accompanying drawings, in which Figure 1 is a diagrammatic View of a radio receiver of the superheterodyne type, inciuding an embodiment of my invention;

Fig. 2 is a View similar to Fig. 1 showingy the preferred embodiment of my invention;

Fig. 3 is a graph, to which reference will be made in explaining the operation of the systems illustrated in Figs. 1 and 2; and

Fig. 4 is a vgraph to which reference will be made in explaining the operation of the system illustrated in Fig. 2.

Referring to Figure 1 of the drawings, an antenna I is coupled to a first detector tube 3 through a band-pass lter 5 constituted by a plurality of series inductors l', 9 and H, and a plurality of shunt-connected tuned circuits each including a condenser I3 and a variable'inductor I5. Also, a variable inductor II is included directly in the antenna ground connection, the last mentioned inductor being tuned by the antennaground capacity. A variable capacitor I9 is preferably included in the antenna circuit in orderl that the system may be lined up" to suit different antennas.

The inductors included in the filter circuit are each provided with a movable core and all of the cores are inter-connected for simultaneous actuation by a tuning device 2|, as indicated by the dotted lines in the drawings. For best results, the cores must have extremely low hysteresis and eddy current losses and, for that reason, I prefer to utilize cores composed of nely comminuted iron and a binder. The specific composition of the core forms no part of the present invention and it need not be described in detail.

The terminals of the filter output circuit are connected, respectively, to the grid 23 and the cathode 25 of the first detector tube. This tube, preferably, is of the equi-potential cathode type including the cathode 25, the control grid 23 and an anode 21, the anode 21 being connected to a source of plate potential over a circuit including the primary winding 29 of an intermediate frequency transformer 3 I.

Since the source of potential itself also forms no part of any present invention, it is exemplified in the drawings by a resistor 33.

The cathode and grid of the first detector tube 3 are connected to the resistor 33 at points negative with respect to the point of connection thereto of the anode 21. A local oscillator 35 is also provided, as is customary, in superheterodyne receivers. This oscillator may also include a thermionic tubeV 31 of the equi-potential cathode type having a cathode 39, a control grid 4|, and an anode 43, the said electrodes being connected to appropriate points on the potential supply resistor 33, as shown in the drawings. The oscillator 35 is provided with a grid circuit tunable over the desired range of frequencies by means of a variable tuning device such as a variable inductance coil 45, which coil is connected to the actuating means 2| of the filter input circuit for simultaneous operation. Preferably, the local oscillations are impressed on the input circuit of the first detector 3 through a small coupling coil 41 in the cathode lead thereof.

The secondary 49 of the transformer 3| forms the input circuit of a second detector 5|, also of the equi-potential cathode type having a cathode 53, a control grid 55, and an anode 51. The several electrodes in the second detector are connected to appropriate points on the potential supply resistor 33, and the primary winding 59 of an audio frequency transformer 6| is included in the plate potential supply connection.

The circuit thus far described, with the exception of the filter input, is typical of superheterodyne receivers. Obviously, as many stages of intermediate-frequency amplification as are necessary may be interposed between the first detector 3 and the second detector 5|. Additional stages of audio freouency amplification (not shown) may be utilized and, as a matter of course, the receiver as actually manufactured commercially contains automatic volume control devices hereinbefore referred to. No necessity is seen, however, for complicating the drawings by the inclusion therein of the elements just mentioned.

In order that automatic tuning may be accomplished, means must be provided whereby the frequency of the locally generated oscillations may automatically be controlled. For this purpose, I provide an auxiliary trimmer condenser B3, one terminal of which is connected to the high side of the oscillator input circuit, and the other terminal of which is connected to the cathode 39 of the tube 31 through a variable impedance device. Specifically, the said variable impedance device is constituted by the space current path in a thermionic tube hereinafter referred to as the frequency control tube. This tube, preferably, is of the equipotential cathode type having a cathode G1, a control grid 69, and an anode 1|, the cathode and anode being connected to suitable spaced points on the potential supply resistor 33. A radio frequency connection between the cathodes 39 and 61 is provided by means of a by-pass condenser 13. Thus, the connection between the trimmer condenser 63 and the cathode 39 is through the space current path of the tube 65 and through the by-pass condenser 13.

The anode 1| may be supplied with a suitable voltage through a choke coil 15, or, if preferred, the choke coil may be replaced by a resistor, as shown in Fig. 2.

In order that the impedance of the space current path in the frequency control tube 65 shall be a function of the tuning of the system, means are provided whereby the grid bias applied to the tube shall be caused to depart from normal in either a positive or a negative direction by an amount proportional to the departure of the intermediate frequency produced in the first detector tube from its predetermined period. For this purpose, I provide a plurality of diodes 11 and 19, having tuned input circuits 8| and 83, respectively, and each being further provided with an output resistor in which unidirectional current flows, this current having an average amplitude proportional to the input to its associated diode. The output resistor of the diode 11 is shunted by an intermediate frequency bypass condenser 81, while the output resistor 89 of diode 19 is shunted by an intermediate frequency by-pass condenser 9|.

The grid 99 of the frequency control tube is connected to a point on the potential supply resistor 33 slightly negative with respect to the point to which the cathode 61 is connected. This connection from the grid S9 to the cathode 61 includes serially the output resistors 85 and 89, the connections being so chosen that potentials developed across the output resistor 85 make the said grid more negative, while potentials developed across the output resistor 89 tend to make the grid less negative. The input circuit of the diode 11, which hereinafter will be referred to as the negative diode, is tuned to a frequency slightly lower (three kilocycles, for example) than the predetermined intermediate frequency and is coupled to the output circuit of the first detector tube 3. The input circuit of the diode 19 is tuned to a frequency slightly higher (three kilocycles higher, for example) than the said intermediate frequency and is also coupled to the output circuit of the first detector tube 3.

The normal fixed bias on the grid of the frequency control tube 65 is so chosen that, when the positive and negative diodes are both functioning to an equal degree the combined effect of the oscillator tuning inductance 45 and the trimmer condenser E3 is such that oscillations are produced which, when beating with a carrier frequency appearing at the mid-point of the band passed by the filter 5, will produce the exact predetermined intermediate frequency. It will be understood that this predetermined intermediate frequency ordinarily falls at the mid-point of the pass range of the tuned transformer 3|.

Assume, now, that an attempt is being made to tune in a desired signal. In such case, the input lter circuit and the oscillator 35 are simultaneously tuned and an intermediate frequency signal is produced in the first detector which, it is assumed, is lower than that to which the intermediate frequency transformer 3| is tuned. (It is also assumed, in such case, that the oscillator is tuned to a frequency higher than the desired signal frequency.) As the oscillator frequency is increased, a small signal potential is impressed upon the negative diode 11. When the receiver is tuned to within say 4 kilocycles of the center of the intermediate frequency band, sufcient signal is impressed upon diode 11 to cause the negative bias on the frequency control tube B5 to increase, thereby tending effectively to remove the trimmer condenser 63 from the oscillator circuit and causing a corresponding increase in the oscillator frequency. This action is cumulative until the oscillator frequency has reached a point of equilibrium at the dip between the two curves marked NEG and POS, shown in Figure 3 of the drawings. these curves being the resonance curves for the circuits 8| and 83, respectively.

If the receiver is tuned to the same signal from the high frequency end of the tuning range, the positive diode 19 controls to progressively reduce the plate impedance of the frequency control tube 65, thus permitting the trimmer condenser G3 to become more and more effective which, in turn, reduces the oscillator frequency. Under these conditions, equilibrium is also obtained, as described in connection with the negative diode.

Since the lter 5 of the input circuit passes a frequency band of 50 to 100 kc., the relative change in alignment of 4 or 5 kc. will not have any bearing on the overall delity of the receiver. Satisfactory performance, therefore, will be obtained automatically just as soon as the system is manually tuned to a frequency whereat the automatic action of the frequency control tube 65 on the oscillator input circuit starts to take place.

An oscillator with variable inductance tuning,

as shown in Fig. 1, is preferable to one with variable capacity tuning in that the trimmer or frequency control condenser 63 may be of a fixed capacity and proper operation will be obtained over the entire tuning range of the receiver.

In a preferred embodiment of the invention, shown in Fig. 2, a noise suppressor circuit which is sharply tuned to the intermediate frequency is provided for preventing the automatic tuning action from taking place before the receiver is tuned to within about 11/2 kilocycles of the desired station. This noise suppressor circuit also permits the receiver to be tuned away from a certain station by rotating the tuning dial through an angle such that, without the automatic tuning control, the receiver would be tuned about 4 kilocycles away from that station. In general, the noise suppressor circuit insures that the frequency control circuit does not begin to control the oscillator frequency tco soon and that it does not keep control of the oscillator frequency too long when tuning the receiver.

Referring to Fig. 2, the receiving system comprises a superheterodyne receiver having a signal channel which includes a first detector 95, an intermediate amplier 91, which may be a screen grid vacuum tube, and a second detector 99 which is preferably a diode. The input circuit of the first detector is coupled to an antenna through a selecting circuit which may be either a fairly broadly tuned radio frequency amplifier or a filter such as the lter described in connection with Fig. 1`

The input circuit of the first detector may include a resistor |93, such as the terminating resi-Stor of the lter 5 (Fig. 1), and a coupling coil |05 and self-biasing resistor |91 connected in series therewith. The self-biasing resistor |01 is preferably shunted by the usual by-pass condenser |09.

An oscillator is provided for heterodyning an incoming signal to a desired intermediate frequency. This oscillator includes an electric discharge tube ||2 and a frequency determining circuit ||3 which consists of an inductance coil ||5 shunted by a variable tuning condenser ||1, the tuning condenser ||1 being variable simultaneously with the tuning of the selecting circuit |9| as indicated by the dotted lines ||9. The cathode |2| of the oscillator tube l2 is connected through a conductor |23 to a source of potential such as a point on a voltage divider resistor |25.

'Ihe plate |21 of the oscillator tube ||2 is connected through a feed-back coil |29 either through a switch |3| to a point on the voltage divider |25 which is positive with respect to the point to which the cathode I2| is connected, or through a switch |32 and a conductor |34 to the anode |36 of a frequency control tube |38. Preferably, a by-pass condenser |28 is provided for lowering the impedance of the oscillator plate circuit for radio frequency currents.

The output circuit of the rst detector 95 is coupled to the intermediate frequency amplifier 91 through an intermediate frequency transformer |33 which is tuned to function as a band pass filter to pass the intermediate frequency carrier and its side-bands.

The output circuit of amplifier 91 is coupled to the second detector 99 through an intermediate frequency transformer |35 which is tuned the same as the preceding transformer |33 to function as a band-pass filter. 'I'he circuit of the second detector 99 includes a resistor |31 which is shunted by an intermediate frequency by-pass condenser |39, one end of the resistor |31 being connected to the cathode |4| of the diode 99.

Audio signals appearing across the resistor |31 are impressed upon the input circuit of an audio frequency amplifier |33 through conductors |45 and |41.

In accordance with one feature of my invention, the control grid |49 of the intermediate frequency amplifier tube 91 is maintained at a high negative potential when the receiver is not tuned to an incoming signal, whereby the amplifier 91 is rendered substantially inoperative. 'I'his high negative potential is applied to the control grid |59 by means of a resistor |5| which is in the plate circuit of a noise suppressor tube |53 which will be described hereinafter.

The biasing circuit for the control grid |49 may be traced from the grid |49 through a winding of the intermediate frequency transformer |33, through a conductor |55 to the noise suppressor resistor |5|, through the resistor |5| and a conductor |51 to a point on the voltage divider |25, and through the votage divider |25 to a more positive point thereon to which the cathode |59 of the amplifier tube 91 is connected. The connection from cathode |59 to the above-mentioned more positive point is through a conductor IBI.

The frequency control circuit is similar to the one described in connection with Figure 1, and includes two diodes |63 and |65 and the frequency control tube |38. As in Figure 1, each diode circuit is tuned and includes an inductance coil shunted by a condenser and connected in series with a resistor, the circuit |69 for diode |63 being tuned to a frequency slightly below the desired intermediate frequency and the circuit |1| for diode |65 being tuned to a frequency slightly above the said intermediate frequency. The two resistors |13 and |15 of the diode circuits are connected in series whereby the voltage drops appearing thereacross control the potential of the grid |61 of the frequency control tube |38. This controls the frequency of the oscillator as described in connection with Fig. 1 providing the switch |3| is closed and the switch |32 is in its left-hand position to connect the trimmer condenser |66 into the circuit.

Since in the circuit of Fig. 2 the oscillator is tuned by a variable condenser rather than by a variable inductor, the trimmer condenser |66 is variable and is connected to be varied simultaneously with the oscillator condenser ||1. The condenser |66 is so connected that as the capacity of condenser ||1 is increased, the capacity of condenser |66 is also increased whereby the ratio of the capacities of the two condensers remains substantially constant. This causes the frequency controlling circuit to have substantially the same control over the oscillator throughout the entire tuning range of the receiver.

If desired, the frequency of oscillator may be controlled by varying the potential applied to its plate |21. This may be accomplished by moving switches |3| and |32 to the positions shown in Fig. 2 whereby the potential applied to the plate |21 depends upon the voltage drop across the resistor |9| in the plate circuit of the frequency control tube |38.

Oscillator is so adjusted that its frequency increases as its plate voltage is increased. Thus, if the receiver is tuned just below a signal, the negative diode |63 will increase the impedance of the tube |38 whereby a decrease in current through resistor |9| will cause a higher voltage to be applied to the oscillator plate |21, and the oscillator frequency will be increased automatically to the correct value for tuning in the said signal.

The intermediate frequency output of the first detector 95 is impressed upon the diodes |63 and |65 through an amplifier tube |11, the input circuit of the amplifier tube |11 being coupled to an output terminal of the intermediate frequency transformer |33 through a coupling condenser |19. The coupling between the output circuit of the amplifier |11 and the inductance coils |69 and |1| of the diode circuits is through a transformer primary winding |8| which is tuned 'to the intermediate frequency.

As in the case of the intermediate frequency amplier 91, the amplifier |11 of the frequency control circuit is maintained in an inoperative condition by means of the noise suppressor circuit when the receiver is not tuned to an incoming signal. The control grid |83 of tube |11 is biased to the required high negative potential for maintaining the amplifier inoperative by means of a connection through a resistor |85 and the conductor |86 to the plate end of the noise suppressor resistor Thus it will be seen that the frequency control circuit cannot function until it is released by the noise suppressor circuit.

Referring now to the noise suppressor circuit, it includes an amplifier |81, a diode rectifier |89, and the noise suppressor tube |53 which may be a screen grid vacuum tube having a cathode |93, a control grid |95, a screen grid |91, and an anode |99. The input circuit of the amplifier tube |81 is coupled to an output terminal of the intermediate frequency transformer |33 through a coupling condenser 20|. The control grid 293 of the amplier tube |81 is biased to a suitable negative potential by means of a connection through a resistor 205 to a point on the voltage divider |25 which is negative with respect to the cathode 291 of tube |81.

The output circuit of amplifier |81 is coupled to the input circuit of the diode |89 through a transformer 209 sharply tuned to the intermediate frequency. The circuit of diode |89 includes a resistor 2| I, shunted by an intermediate frequency by-pass condenser 2|3, this resistor functioning to control the potential of the control grid of the suppressor tube.

The control grid |95 is connectedthrough a conductor 2|5 and a variable tap 2|1 to a point on the resistor 2||. The cathode end of the resistor 2|| is connected to the cathode |93 of noise suppressor tube |53 through a circuit which includes at least a portion of the second detector resistor |31 whereby a trigger action of the noise suppressor is obtained as will be fully explained hereinafter. This circuit includes a conductor 2 |'9, the resistor |31, and a conductor 22|.

In some cases, the use of a filter between the resistor 2H and the grid |95 may improve the operation of the receiver by preventing any audio frequency signals from reaching said grid. Such a filter may consist of a series resistor 268 and a shunt condenser 2 0.

The plate |99 of the noise suppressor tube |53 is connected to one end of the noise suppressor resistor |5| through the secondary winding of a transformer 223 which supplies the proper alternating voltage to the plate |99. The other end of the resistor |5| is connected to the cathode |93 whereby resistor |51 is connected in the plate circuit of the tube |53 so that the voltage drop thereacross is determined by the value of the plate current. Resistor |5| is preferably shunted by an audio frequency bypass condenser 2|2. From the previous description of the grid biasing circuits for the amplifiers 91 and |11, it will be seen that a large fiow of plate current through the resistor |5| will bias these lamplifiers to an inoperative condition.

The above-described circuit will operate in a fairly satisfactory manner with the second detector resistor |'31 omitted from the noise suppressor circuit since an incoming signal will cause the control grid |95 of the suppressor tube to become more negativey thereby reducing the fiow of current through the noise suppressor resistor |5| and lowering the negative potentials applied to the control grids of the amplifiers 91 and |11. It is desirable, however, to have the reduction in grid potential of the amplifier tubes 91 and |11 more rapid and positive than is possible with the resistor 21| alone controlling the potential of grid |95.

Therefore, in accordance with one feature of my invention, I include the resistor |31 in the circuit coupling the diode |89 and the suppressor tube |53 for providing the noise suppressor circuit with a trigger action. It will be apparent that the potential of the control grid |95 of the suppressor tube depends upon both the signal supplied through the diode |89 and upon the signal supplied through the second detector 99 which is under the control of the noise suppressor. In other words, the voltage applied to this control grid |95 is the sum of the voltage drops across the resistors 2i and |31.

As soon as a signal passes through the transformer 299 f the noise suppressor circuit, the resulting voltage drop across resistor 2|| causes a reduction in the plate current of tube |53. This causes a suicien't reduction in the negative bias of the amplifier 91 in the signal channel to permit a certain amount of signal to pass therethrough and produce a voltage drop across resistor |31. This causes the control grid |95 of the suppressor tube to be made still more negative and the plate current through resistor is still further reduced. This action continues until the plate current of tube |53 has been reduced practically to zero and the amplifiers 91 and |11 are operating with their control grids properly biased for amplifying the incoming signal.

An automatic volume control or AVC circuit is shown schematically at 225. This circuit may be any one of the various well known AVC circuits and is of importance in keeping the voltage which is applied to the tuning control and noise suppressor circuits below a certain predetermined value, whereby the suppressor circuit releases only when the intermediate frequency is near the resonant point of the sharply timed transformer 299.

The operation of the system illustrated in Fig. 2 will be more clearly understood by referring to Figs. 3 and 4. In Fig. 3 the dotted line 221 represents the resonance curve of the tuned transformer 299 in the noise suppressor circuit. As previously mentioned, the two solid line curves show the resonance characteristics of the two diode circuits marked NEG. and POS., respectively.

In Fig. 4 the actual intermediate frequency produced by the oscillator output beating with an incoming signal as the receiver is tuned is plotted against the intermediate frequency that would have been `produced if the oscillator had not been under the control of the frequency control circuit. It may be noted that the latter frequency is almost directly proportional to the rotation of the oscillator tuning condenser ||1 and the tuning knob of the receiver. The curve is plotted for the condition where the receiver is being tuned from a frequency lower than that of the signal being tuned in.

Referring to Fig. 4, it will be noted that in `the region of 165 kilocycles, for example, the oscillator is not under the control of the frequency control circuit. As the oscillator frequency is increased to within one and one half kilocycles of the 175 kilocycle intermediate frequency the oscillator is still not controlled by the frequency control circuit because up to this point the noise suppressor circuit has maintained the amplifier tube |11 in a blocked or inoperative condition. At one and one half kilocycles from the 115 kilocycle intermediate frequency, however, sufficient energy passes through the sharply tuned noise suppressor transformer 299 to initiate the above described trigger action whereby the blocking potential is removed from the amplifier |11. Energy-is instantly supplied to the two frequency control diodes, |53 and |65, the negative diode |63 receiving the greater part of the energy whereby the frequency of the oscillator is increased to a value such that the intermediate frequency is brought to within a fraction of a kilocycle of the 175 kilocycle value.

At the same timle that the frequency control circuit is released by the noise suppressor, the blocking potential is removed from the intermediate frequency amplifier 91 and the signal is heard. It will be seen that the oscillator frequency has been changed automatically to a value such that the signal is transferred through the intermediate frequency signal channel without any attenuation or distortion of the signal side-bands.

Further rotation of the oscillator tuning condenser ||1 causes the frequency of the oscillator output to increase very slowly since it is now under the control of the frequency control circuit. Therefore, the tuning dial of the radio receiver may be rotated through a considerable angle without changing the tuning of the receiver substantially.

The receiver is tuned to a different station by rotating the tuning condenser ||1 of the oscillator sufficiently to change the intermediate frequency approximately one and one half kilocycles, at which value the energy transferred through transformer 299 to the noise suppressor diode |89 becomes so small that the trigger action previously described is reversed and blocking potentials are applied to the control grids of the amplifier tubes 91 and |11.

It will be understood that when tuning from a higher frequency to a lower frequency the action of the circuit is the same as described above. While specic values have been referred to in describing miy invention it should be understood that they have been referred to merely to make my invention more clearly understood and that in many instances, other values will be preferred.

Various modifications may be made in my invention without departing from the spirit and scope thereof, and I desire, therefore, that only such limitations shall be imposed thereon as are necessitated by the prior art and set forth in the appended claims.

I claim as my invention:

1. In a radio receiver of the superheterodyne type, a first detector provided with a modulated signal input circuit, solely a single local oscillator feeding the detector, the oscillator being of the type having only a single tube, a tuning device for the detector and oscillator, means for varying inunison the frequency of said oscillator and said detector input circuit in accordance with a movement of said tuning device, said input circuit having a pass band of the order of kilocycles, and means for further changing the frequency of said oscillator automatically in response to said detector input circuit being tuned within a predetermined frequency range on either side of the frequency of an incoming signal, said last means including a pair of rectiiiers in opposed relation and coupled to the detector output for deriving a direct current voltage from the detector output energy when the frequency thereof departs from an operating value.

2. In a radio receiver comprising means for converting an incoming radio frequency signal to an intermediate frequency signal, said means including -a detector and an oscillator, means including uni-controlled tuning devices for said detector and oscillator for varying the frequency of said oscillator and detector over a predetermined tuning range, said detector having a signal input circuit whose pass band width is of the order of 100 kilocycles, and means for further changing the frequency of said oscillator automatically in response to said detector being tuned close to the frequency of'an incoming signal by said varying means, said last means including a pair of opposed rectiers coupled to the detector output and producing a direct current voltage upon said close tuning, and a device utilizing said voltage to effect said frequency change.

3. A receiving system comprising means for collecting a modulated carrier wave, a local oscillator consisting solely of a single tube for heterodyning said carrier wave to an intermediate frequency signal, tuning means for said oscillator', a frequency control means, having an input circuit arranged to have the intermediate signal impressed thereon, for changing the frequency of said oscillator, a network for utilizing the intermediate signal, and means auxiliary to said control means for controlling the transmission efficiency of said input circuit in a sense to render said frequency control means effective when and only when, said intermediate frequency differs from a desired intermediate frequency by at least a predetermined amount, said auxiliary means being fed With the intermediate signal but being out of said network.

4. A receiving system comprising means for collecting modulated carrier energy, a local oscillator consisting solely of a single tube for heterodynng said carrier energy toV a desired intermediate frequency signal, tuning means for said oscillator, frequency control means including an input circuit responsive to said intermediate frequency signal for maintaining a constant frequency difference between said oscillator and the carrier energy of a received signal, a network for utilizing the intermediate signal, and means auX- iliary to said controlA means for automatically regulating the transmission eilciency of the input circuit soY as to render said frequency control means effective only when said oscillator is tuned close to a frequency which beatsv with said signal to produce said intermediate frequency, said auX- ili a ry means being fed with the intermediate signal but being out of said network.

5. A receiving system comprising means for collecting a modulated carrier wave, a local oscillator for heterodyning said carrier wave to an intermediate frequency signal, tuning mea-ns for said oscillator, frequency control means for changing the frequency of said oscillator, means including a coupling tube for impressing said intermediate frequency signal upon said control means, and means for rendering said coupling tube effective only when said signal has a carrier frequency close to a predetermined frequency, said last means including a circuit sharply tuned to said predetermined frequency.

6. A receiving system comprising means for collecting a modulated carrier wave, a first detector having an input network coupled to said collecting means and an output circuit, a local oscillator of the type consisting only of a single tube coupled to said rst detector for heterodyning said carrier wave to an intermediate frequency signal, said. oscillator having a single tank circuit including a variable reactance device for varying its frequency, a tuning. device mechanically connected tosaid variable rfeactance wherebythe frequency of said oscillator may be changed by moving said tuning device, an intermediate frequency transformer coupled to the output circuit of said rst detector and tuned to a predetermined intermediate frequency, said input network having a substantially wider pass band than said transformer, and means for holding the carrier frequency of said intermediate frequency signal substantially constant in the region of said predetermined frequency while moving said tuning device through a predetermined distance, said last means including a pair of rectiers, coupled to said transformer, having direct current output circuits connected in opposition thereby to produce a direct current voltage upon a departure of said signal from said predetermined frequency, and a device, other than said local oscillator, responsive to said voltage for adjusting the frequency of the tank circuit supplementally to said variable reactance device.

'1. A receiving system comprising means for collecting a modulated carrier Wave, a lirst detector having an output circuit, a local oscillator coupled to said rst detector for heterodyning said carrier wave to an intermediate frequency signal, said oscillator including a variable reactance device for varying its frequency, a tuning device mechanically connected to variable reactance whereby the frequency of said oscillator may be changed by moving said tuning device, an intermediate frequency transformer coupled to the output circuit of said first detector and tuned to a predetermined intermediate frequency, and means for holding the carrier frequency of said intermediate frequency signal substantially constant in the region of said predetermined frequency while moving said tuning device through a predetermined distance, said variable reactance device in said oscillator being a variable inductor, and said last means including va xed condenser connected in series with the space current path of a space discharge device 4and shunted across said inductor.

8. A receiving system comprising means for collecting a modulated carrier wave, a first detector having an output circuit, a local oscillator coupled to4 said first detector for heterodyning said carrier Wave to an intermediate frequency signal, said oscillator including a variable reactance device for varying its frequency, a tuning device mechanically connected to said variable reactance whereby the frequency of said oscillator may be changed by moving said tuning device, an intermediate frequency transformer coupled to the` output circuit of saidfirst detector and tuned to a predetermined.intermediate frequency, and means for holding the carrier frequency of said intermediate frequency signal substantially constant in the region of said predetermined. frequency while moving said tuning device through a predetermined distance, said variable reactance device in said` oscillator being a variable condenser, and said last means including a variable condenserfconnected inserieslwith the space current path of a space` discharge device and. shunted across saidrst variable condenser, said two variable4 condensers being mechanically coupled for simultaneous operation through a unitary control.

9. A receiving system comprising a variable band-pass filter having input terminals and output terminals, a signal supply circuit connected to said input terminals, a first detector coupled to said output terminals, a tunable oscillator coupled to said detector for converting an incoming signal to an intermediate frequency'signal, and

frequency control means for'maintaining a constant frequency difference between said incoming signal and said oscillator after said oscillator has been tuned to a frequency differing from the frequency of said signal by -a predetermined amount, a second detector, and an intermediate frequency filter circuit coupling said rst detector and said second detector, said filter circuit having a certain pass range, said variable band-pass filter having a pass range substantially greater than the pass range of said intermediate frequency lter whereby changes in the oscillator frequency produced =by said frequency control means do not cause mis-alignment of said two lters.

10. In a receiving systemrhaving a signal selector circuit for selectively receiving modulated carrier waves having a predetermined frequency spacing, means including a local oscillator for heterodyning a selected carrier Wave to an intermediate frequency signal, said oscillator being of the type having only a single tube provided with a tank circuit which is tunable over a predetermined tuning range for selecting the desi-red carrier wave, and control means including a pair of resonant rectifier networks, oppositely mis-tuned by a desired frequency value from said intermediate frequency, and connected in opposition to produce a direct current voltage for automatically changing Ithe frequency of said oscillator to produce said signal in response to tuning the receiver closer .to one of said carrier waves `than to an adjacent carrier wave by a predetermined number of kilocycles an 'intermediate frequency signal network coupled to said pair of resonant networks to transmit intermediate frequency signals thereto, said signal selector circuit having a substantially wider pass band than said intermediate frequency network.

1l. In a radio receiver having a signal selector circuit for selectively receiving carrier waves having a frequency spacing of kilocycles, means for converting an incoming carrier wave to an intermediate frequency signal, said means including an oscillator of the type having only a single tube provided with a tank circuit, means in said tank circuit for varying the frequency of said oscillator over a predetermined range for selecting one of said carrier waves, and control means including a pair of resonant rectifier networks, oppositely mistuned yby a desired frequency value from said intermediate frequency, and connected in polarity opposition to produce a voltage for further changing the frequency of said oscillator automatically in response to said receiver being tuned closer than 5 kilocycles to the desired carrier wave an intermediate frequency signal network coupled to said pair of resonant networks to transmit intermediate frequency signals thereto, said signal selector circuit having a substantially wider pass band than -said intermediate frequency network.

l2. In a radio receiver for selectively receiving carrier waves having a frequency spacing of N kilocycles, means for converting an incoming carrier wave to an intermediate frequency signal, said means including an oscillator of the type consisting of a single tube having a tunable tank circuit, means in said -tank circuit for varying the frequency of said oscillator over a predetermined range for selecting one of said carrier waves, a network utilizing said sign-al, resonant control means having intermediate signals impressed thereon, but being out of the utilizing network, for further ,changing the lfrequencyof said oscillator automatically in response to said receiver being tuned closer than kilocycles to the desired carrier wave, and auX- iliary means, responsive to the variation in signal intensity at the converting means output, for regulating the impression 4of said intermediate signals on said control means.

13. In a superheterodyne receiver of the type including a signal input circuit, a local oscillator circuit having only la single tube pro-vided with a tank circuit which includes main and auxiliary frequency determining elements, a frequency changer, and an intermediate frequency network tuned to a carrier frequency F1, said signal input circuit having a substantially Wider pass band characteristic lthan said intermediatenetwork, a resonant circuit tuned -t-o a frequency slightly below Fi, means to rectify alternating vol-tage developed in the resonant circuit, a second resonant circuit tuned to a frequency slightly above Fi, means to rectify alternating voltage developed in the second circuit, means to supply energy fr-om the intermediate frequency network to said resonant circuits, and means responsive to the difference between said rectified voltages to vary the effect o-f said auxiliary frequency determining element of the local oscillator circuit in such a sense as to cause the frequency of energy transmitted through the intermediate frequency network to approach more nearly to Fi.

114. In combination in a superheterodyne receiver -o-f the type including a tunable signal circuit and a tunable local oscillator circuit of the type consisting only of a single tube having a tunable tank circuit, means for simultaneously tuning both signal and oscillator circuits through frequency ranges which constantly differ by a predetermined beat frequency, an auxiliary network comprising a pair of resonant circuits, a network, tuned .to said beat frequency, feeding beat energy to said auxiliary network, said signal circuit having a relatively wider pass band than said beat frequency network, each resonant circuit including a rectifier, means for impressing the beat frequency energy upon said resonant circuits, one of said resonant circuits being tuned to a frequency differing from :the beat frequency by a predetermined frequency value, the other resonant circuit being tuned to a frequency differing from the beat frequency by the same frequency value but in an opposite direction-and means responsive to the differential direct current iiow of said rectifier circuits for varying the tuning of said local oscillator -tank circuit in a sense such that .the energy impressed upon said pair of resonant circuits is equal to said bea-t frequency.

15. A modulated high frequency signal receiving system which includes, in combination, a converter network having a, signal input circuit on which are impressed collected signals and an output circuit, a local oscillator network electrically associated with said converter for heterodyning said collected signals to an intermediate frequency signal, said oscillator network being of the ytype consisting only of a single tube having a resonant tank circuit which includes a variable reactance device for varying its frequency through a relatively wide frequency range, said converter network .including a second variable reactance ldevice for l varying vits frequency,

through a relatively wide frequency range of different limits, a tuning device mechanically coupling s-aid variable reactances whereby the frequencies of said oscillator and converter networks may be changed by adjust-ing said tuning device, an intermediate frequency utilization network coupled to the converter output circuit and tuned to a predetermined intermediate frequency, said signal input circuit being of a substantially wider pass band than the said intermediate network, means for holding the carrier frequency of said intermediate frequency signal substantially constant in the region of s-aid predeterminad frequency while adjusting said tuning device through a predetermined distance and means coupled between the converter output circuit and said holding means for automatically regulating the transmission of intermediate frequency signals to the latter.

16. A modulated high frequency signal receiving system which includes, in combination, a converter network having a signal input circuit on which are impressed collected signals and an output circuit, a local oscillator network electrically associated with said converter for heterodyning said collected signals to an intermediate frequency signal, said oscillator network including a variable reactance device for varying its frequency 'through a relatively wide frequency range, said converter network including a second variable reactance device for varying its frequency through a relatively wide frequency range of different limits, a tuning device mechanically coupling said variable reactances whereby the frequencies of -sa-id oscillator and converter networks may be changed by adjusting said tun-ing device, an intermediate frequency utilization network coupled to the converter output circuit and tuned to a predetermined intermediate frequency, said signal input circuit being of a substantially wider pass band than the said intermediate network, and means for holding the carrier frequency of said intermediate frequency signal substantially constant in the region of said predetermined frequency while adjusting said tuning device through a predetermined distance, lsaid last means comprising an auxiliary frequency determining reactance electrically associated with said oscillator variable reactance, and resonant means, responsive to a frequency shift of said intermediate frequency signal from said predetermined intermediate frequency, for regulating the effect of said auxiliary reactance on the oscillator network frequency and auxiliary means connected between the converter output circuit and said last named resonant means for automatically preventing the transmission of intermediate frequency signals to said resonant means when said tuning device is adjusted beyond said predetermined distance.

17. In a radio receiver of the superheterodyne type, means for selecting a desired modulated carrier signal, a local oscillator network including means for tuning it to ya frequency differing from the signal frequency by a desired operating intermediate frequency, an intermediate frequency transmission channel coupled to the output circuit of lthe selecting means, means for vdemodulating the signals transmitted through said channel, an automatic frequency control circuit, responsive to a departure in the frequency of the intermediate signals from said operating frequency for automatically adjusting the ioscillator frequency supplementally of the tuning means, mean-s feeding intermediate signals from said channel to said control circuit, an auxiliary control circuit, responsive to a departure of a predeterminedv magnitude of said intermediate signals, for automatic-ally preventing the transmission of said intermediate signals to said frequency control circuit.

18. In a radio receiver of the type dened in claim 17, an additional means, responsive -to operation of said auxiliary control circuit for preventing transmission of intermediate signals through saidchannel to a demodulator.

19. A radio receiver having an adjustable tuning means for selecting any one of a number of different carriers within a range of frequencies, carrier-responsive means actuated by any inaccuracy in the operation of said tuning means which substantially compensates therefor, and means whereby the ratio of said compensation to said inaccuracy is rendered substantially constant regardless of the frequency of the selected carrier.

20. A radiov receiver having manually controlled tuning means for selecting any one of a number of different carriers within a range of frequencies, means actuated by any inaccuracy in the operation of said tuning means which su-bstantially compensates therefor, and means whereby the ratio of said compensation to said inaccuracy Iis rendered substantially constant regardless of the frequency of the selected carrier.

21. The method of automatically compensating for inexact resonance adjustment of a radio receiver variably tunable to selectively receive any one of a number of different carriers throughout a wide range of frequencies, which comprises producing a reactance variati-on the magnitude and sense of which depend respectively upon the magnitude and sense of the error in the reson-ance adjustment of said receiver when approximately adjusted to receive any carrier within said frequency range, .applying said reactance variation to produce an alteration of the effective resonance adjustment of said receiver, and so controlling the effect of said reactance variation throughout said frequency range that the ratio of said alteration to the magnitude of the error in resonance adjustment is substantially independent of the frequency of the selected carrier.

22. The method of automatically compensating for inexact resonance adjustment of a radio receiver variably tunable 'to selectively receive any one of a number of different carriers throughout a wide range of frequencies, which comprises producing a reactance variation the magnitude and sense of which depend respectively upon the magnitude and sense of the error in the resonance adjustment of said receiver when approximately adjusted to receive any carrier within said f-requency range, applying said reactance variation to produce =an alteration of the effective resonance adjustment of said receiver, `and so controlling the effect of said reactance variation throughout said frequency range that the ratio of said alteration to the magnitude of the error in resonance adjustment is substantially constant.

23. A radio receiver of the superh'eterodyne type including a vacuum-tube oscillator manually controlled means for approximately adjusting said oscillator to select any one of a number of carriers within a range of frequencies, means including a reactance for varying the frequency of said oscillator to substantially compensate for inaccuracy in the adjustment of said adjusting means, and means for yapplying a portion of said reactance to said oscillator such that the ratio of said compensation to said inaccuracy is rendered substantially constant regardless of the frequency of the selected carrier.

l24. A superheterodyne radio receiver having in combination, `an intermediate-frequency amp'lier, means including an oscillator adjustable to select any carrier within a rang-e of frequencies an-d to convert said carrier to said intermediate frequency, a pair of resonant circuits tuned respectively above and below said intermediate frequency, rectifiers connected to said circuits, a resistance network through which the currents produced by said rectiers flow to produce a direct-current potential Whose magnitude land polarity are determined by the magnitude and sense of any inaccuracy in the adjustment of said oscillator, a vacuum tube having a grid, a connection for applying said potential to said grid, and means for coupling said vacuum tube to said oscillator such that the potential resulting from said inaccuracy automatically produces an alteration in the frequency of said oscillator which substantially compensates for said inaccuracy, said coupling means being of 'such nature that the ratio of said compensation to said inaccuracy is substantially independent of the frequency of the selected carrier.

25. A high-frequency receiving system including a resonant circuit, a control for tuning said circuit to select any carrier with-in la range of frequencies, means including an automatically varying reactance to substantially correct for inaccuracy in the setting of said control, and means for applying |a portion of said reactance to said circuit such that the ratio of said correction to said inaccuracy is substantially independent of the frequency of the selected carrier.

26. A superheterodyne radio receiver having in combination, an intermediate-frequency ampli- Iier, means including an oscillator adjustable to select any carrier Within a range of frequencies and to convert isaid carrier to said intermediate frequency, means coupled to the output of said intermediate-frequency amplier for producing a direct-current potential Whose magnitude and polarity are determined by the magnitude and sen-se of any inaccuracy in the adjustment of said oscillator, a vacuum tube having a grid, a

connection for applying sai-d potential to said grid, and means for coupling said vacuum tube to said oscillator such that the potential resulting from said inaccuracy automatically produces an altera-tion in the frequency of said oscillator which substantially compensates for said inaccuracy, said coupling means being of such nature that the ratio of said compensation to said inaccuracy is substantially .independent of the frequency of the selected carrier.

GEORGE L. BEERS. 

